Sexual assault is prevalent within today’s society with 18% of women reporting sexual assault within their lifetime (1). Physical evidence collected from a forensic examination may include an intimate swab. The standard method used for sperm isolation is differential lysis however, the high abundance of vaginal epithelial cells on vaginal sexual assault swabs complicates the protocol. This factor results in mixed DNA profiles with an overabundance of female DNA present in an autosomal STR profile. Mixed STR profiles make it difficult to interpret the male DNA profile and therefore cannot always be used in court to identify a perpetrator. An antibody-based method for spermatozoa extraction using antibody conjugated immunomagnetic beads to select for sperm could be used as a method of enrichment, producing a higher yield of recovered male DNA. To achieve this, sperm-specific antibodies are needed to selectively bind to the sperm when in an epithelial/sperm cell mixture.
This study aimed to identify the capability of 3 antibodies, α-SPAM1, α-SPACA1, and α-ZPBP with a secondary antibody Goat α-Rabbit IgG (H+L) Secondary Antibody, Alexa Fluor Plus 488 through flow cytometry. Canto™ II CA flow cytometer was used for the visualisation of sperm/vaginal epithelial cell cross-reactivity with the antibodies to determine the cell sensitivity and selectivity. Optimisation of the flow cytometry protocol was undertaken for both the epithelial and sperm cells. The antibodies had >20% cross-reactivity to the sperm cells and >30% to the vaginal epithelial cells however, the epithelial cells had a higher autofluorescence than expected with >30% positive unstained epithelial cells
